Cable modems and the DOCSIS (Data Over Cable Service Interface Specification) standard have made delivery of digital services over hybrid fiber coaxial (HFC) cable television systems possible. Digital data delivery of Internet data, video on demand movies, telephony, telephony over the Internet, interactive games, upstream delivery of security camera digital photos to security services and a host of other applications is becoming possible. These services are very useful and valuable, some more than others. Some services take more bandwidth than others. Video on demand over the HFC system is seen by many as the killer application for the future. Video and movies, even when compressed with MPEG, take large amounts of bandwidth and substantially more bandwidth than delivery of Internet data. A general rule of thumb for MPEG-2 compression is 3 to 3.5 MB/s per video stream. Statistical multiplexing of a 3.5 MB/s stream over a 38 MB/s channel is poor. Increasing the rate per customer premises equipment can improve statistical multiplexing dramatically. Although this does not benefit the customer, it is of great benefit to the service provider cable system operators who buy cable modems and cable modem termination systems.
A technique called port trunking or link aggregation has been used in prior art telephone systems and other data communication systems. Two relevant standards for port trunking outside the world of HFC systems exist: IEEE 802.3 ad for link aggregation over Ethernet; and Multilink-PPP as described in RFC 1990.
Neither of these standards mention DOCSIS nor could they be used in a DOCSIS system. This is because both of these standards require point-to-point links, and DOCSIS is a point-to-multipoint link environment. There are no point-to-multipoint versions of port trunking specified anywhere to the knowledge of the inventors.
HFC systems are shared by multiple users, so the bandwidth available to each customer is not unlimited. A DOCSIS QAM 64 channel has a bandwidth of 6 megahertz (MHz) and a payload capacity of 27 megabits per second (MB/s). QAM 256 modulation is used in the more advanced versions of DOCSIS, but still the channels are 6 MHz wide and the payload capacity is only 38 MB/s. In Europe, QAM 64 channels are 8 MHz in bandwidth and 38 Mb/s, and QAM 256 channels have payload capacity of 51 MB/s. Each channel has its own frequency slot.
The payload capacity represents the total aggregate bandwidth available shared by all the cable modems (CM) that are tuned to that particular channel. The payload capacity also represents the maximum burst rate that is available to a single CM at any moment in time. Some services require more payload delivery capacity than this.
Current DOCSIS only provides for increasing the aggregate capacity only by allowing the transmission of multiple channels at the CMTS (cable modem termination system), or headend, and splitting the population of cable modems so that some are tuned to each of the available channels. This does increase the aggregate capacity across a given population size of CMs, but does not increase the burst capacity to any single CM. So that problem still remains, and it is a significant problem for the best customers who have high demand for data.
DOCSIS does have a mechanism to direct CMs tuned to one downstream (DS) channel to tune to another DS channel for load balancing purposes, but this method takes many 10s of milliseconds during which the CM is unable to receive any data while it is re-tuning its receiver, waiting for another invitation to perform ranging (ranging means DOCSIS ranging and equalization followed by downstream messages to the CMs indicating how they should adjust their timing, frequency, phase, power and including upstream equalization coefficients for use in developing new upstream equalization filter coefficients and will hereafter be referred to simply as ranging) on the new channel and performing the ranging process again during the designated ranging window on the new channel.
It is desirable to increase the traffic rate to CMs for three reasons:    1. to increase the average data rate available to all connected CMs since the data rate of services rises over time;    2. to increase the burst rate to a single CM; and    3. to increase the level of statistical multiplexing of data traffic on the channel.
The existing DOCSIS protocols only address problem #1 listed above. Problems #2 and #3 listed above can only be resolved by increasing the instantaneous available bandwidth to a single modem.
There are only two methods to increase the capacity to a single device:    1. increase the capacity per channel; or    2. increase the number of channels available to cable modems which have the ability to tune to multiple channels simultaneously and share capacity among them.
Other workers skilled in the art such as engineers at Broadcom are attacking this problem of increasing the capacity of a channel so as to increase the maximum burst rate to a single CM by attempting other approaches than are described herein. Generally, these other approaches involve physical layer techniques. These techniques include: increasing the symbol rate; increasing the modulation order such as by moving from QAM 256 to QAM 512 or QAM 1024; improving the forward error correction encoding so as to be able to detect and correct the larger number of errors which result when more data is sent down a channel of a fixed bandwidth which is already transmitting at maximum capacity; or possibly changing the modulation scheme. One or more of these techniques may be in use now in Broadcom products. Other link layer techniques such as data compression are also being investigated.
Moving to higher density constellations such as QAM 512 and QAM 1024 requires a very quiet channel and high signal to noise ratio (high quality HFC system and good noise suppression) or a high degree of forward error correction and loss of throughput because of the larger number of error detection and correction bits added to the payload data stream. Quiet channels with high signal to noise ratio are hard to achieve and high enough S/N may be impossible to achieve in some older systems.
All of these techniques or approaches have one shared major flaw besides the loss of throughput and stringent requirements placed on the HFC system for high signal to noise ratio. They are not backward compatible, which means they render obsolete all the old single DOCSIS channel CMs on an HFC system that were not designed with these techniques in mind and would require replacement of the CMTS. This is a huge problem, because cable operators have millions of dollars invested in their existing inventory of CMs and CMTS and they do not want to spend similar amounts of money or more to replace it all. Outside of this patent application, nobody that the applicants are aware of has either developed or proposed the use of port trunking in a DOCSIS system.